I. Field of the Invention
This invention relates generally to water soluble compositions having complex silicates and magnesium sulfate used primarily for water treatment systems. More specifically, this invention relates to compositions and methods used in water treatment systems of paint spray booths.
II. Description of the Background Art
Modern industrial paint spraying is performed in special paint spray booths. The booths generally are enclosed and have a circulating water system which is used to scrub paint overspray particles from the air. Some paint spray booths have a water washed floor and devices for mixing water and air to promote the removal of paint overspray particles from the air by the water. Complex silicate minerals, such as diatomite, and other inert materials are known to be used in paint spray booths water recirculating systems to improve the paint "killing" abilities of such systems. Paint killing as used herein refers to detackifying the paint particles, or eliminating their adhesive properties.
Generally it is preferable to provide a concentrated slurry form product for ease in handling, transportation and elimination of dust. Slurry form material is easier to handle because it may be added to water by merely pumping the material into the water recirculating system. Transportation of slurry materials is preferred because it can be shipped by tank truck in bulk or drum form. One of the most important features of providing complex silicate material based paint denaturant in slurry form is that it eliminates the problems associated with using fine particulate materials in paint spray booths.
Bentonite clay is commonly used for this purpose due to its favorable properties in absorbing or adsorbing live paint. However, bentonite's tendency to swell when mixed with water makes it inappropriate for use as a slurried material. Bentonite can only be slurried to less than 5% solids concentration in water before it becomes a semi-plastic material which is not pumpable. Heretofore, it has not been economically feasible to provide paint denaturants including bentonite in a slurry form because the low solids content require excessive amounts of concentrate be added to the water recirculating system. The low levels of solids achievable would also necessitate excessive handling and transportation costs to use bentonite in slurry form. Bentonite is particularly effective in absorbing polar components of paints such as alcohol and other molecules with hydroxyl groups such as acrylic polymers.
Kaolinite is known to be used in some paint denaturant compositions but it does not have favorable absorptive properties. Kaolinite does not swell in water as does bentonite and it is more stable in aqueous solutions than bentonite. Kaolinite is used in paint denaturant compositions to separate other inert materials such as bentonite or talc thereby achieving better dispersion of the inert materials. Kaolinite is effective in absorbing some partially polar components such as ketones to a limited extent. However, it's lack of good paint killing or paint absorption properties generally makes kaolin an inappropriate material for a paint denaturant.
Talc is known generally as a good oil and solvent absorbing material, However, talc particles are relatively large, about 10 microns in size, and tend to settle out of a slurry mixture forming a non-homogeneous dispersion. It has been found that mixing kaolin clay with talc aids in forming a suspension due to the thixotropic properties of the kaolinite. Talc tends to be best at absorbing non-polar materials such as aromatic solvents and is useful in some paint denaturing compositions.
Diatomite, or kieselguhr, is another complex silicate mineral which is an effective absorptive material useful for encapsulating paint particles. However, diatomite is a non-swelling mineral which requires a thixotropic material such as kaolinite to permit it to become suspended as a slurry. Diatomite is particularly effective at adsorbing and absorbing non-polar type materials such as oily substances including toluene and melamine.
Other inert materials such as mica and trilite clay are ocassionally used in paint denaturing compositions but are objectionable due to their fiberous nature and their classification as hazardous materials when used in dry form because they are in the family of asbestiform materials.
Combinations of the above materials including especially bentonite have been experimented with however the viscosity of bentonite in solution is a limiting factor to using such combinations as slurries. Once several of the above materials are combined and include bentonite the percent of solids in a liquid concentrate, or slurry, must be maintained below about 7% by weight or the composition becomes plastic, and difficult to pump.
The most important factor in evaluating paint denaturant performance is the degree to which it detackifies the paint overspray, or "kills" the paint. A properly killed paint will not adhere to the paint spray booth surfaces or the water recirculating equipment. A problem with prior paint denaturants is the residual tackiness of the killed paint overspray residue. The residue of some paints may over time redevelop tackiness. The residue of some paints may also become tacky if exposed to solvents used to clean or purge the paint spraying equipment.
A nonsilicate paint denaturant comprising an aqueous solution of iron sulfate, magnesium sulfate or manganese sulfate either with or without a surfactant is disclosed in U.S. Pat. No. 4,294,617 to Schlicklin, et. al., which is limited to denaturing water-base paints. The compositions disclosed in the Schlicklin patent is not intended to be used with solvent based paints and does not suggest the combination of such compounds with complex silicate minerals.